In November, Bilic was removed from his position in the dugout at the London Stadium due to the club's poor form in the Premier League, and replacement David Moyes has since recorded eight points from eight top-flight fixtures.
The Hammers have been linked with additions in the centre of the park, and Bilic has acknowledged that he wished he had done more to sign a player who could sit in front of his defence.
The 49-year-old told Goals On Sunday: "Of course, there are things that I could have done differently. I should have maybe insisted on some of the positions more. I wanted, and the club are lacking, a holding midfielder.
"I'm not criticising the quality of the players but some of the players playing in that position are more box to box. The last proper one was Alex Song. He didn't play a lot due to his knee situation.
"I wanted to sign one but I didn't really insist on it that much. However, I have no regrets at all. I enjoyed my time there and only have fond memories."